Slip-clutch

ABSTRACT

A slip-clutch for use with a tape winding-up mechanism of a tape recording and reproducing apparatus. A cylindrical drum is provided on a pulley for receiving input force of the clutch and a length of rope is wound around the drum in frictional torque transmitting sliding engagement therewith. The rope has opposite ends connected to a disc rigidly secured to an output shaft of the clutch whereby substantially constant torque is transmitted from the drum to the disc regardless of variation in coefficient of friction between the driving and driven members.

Unlted States Patent 1151 3,691,791 Yoshii 1 51 Sept. 19, 1972 [54]SLIP-CLUTCH 971,335 9/1910 Williamson, Jr. ..64/30 R 988,182 3/1911Ewald ..64/30 C [72] Invent Ymhfi Neyagawa Japan 1,793,515 5/1957l-lunstiger et al ..64/30 0 Assignee= Matsushita Electric Industrial(30., 3,043,091 7/1962 Hodges ..64/30 R x Ltd., Osaka, Japan PrimaryExaminer-Allan D. Hermann [22] Flled' Sept 1970 Attorney-Stevens, Davis,Miller & Mosher [21] App]. No.: 70,036

[30] Foreign Application Priority Data Sept. 10, 1969 Japan ..44/73089Jan. 27, 1970 Japan ..45/7928 52 us. 01. ..64/30 E [51] Int. Cl ..Fl6d7/02 [58] Field of Search ..64/3O R, 30 C, 30 E [56] References CitedUNITED STATES PATENTS 2,859,601 11/1958 Evans ..64/30 R [5 7] ABSTRACT Aslip-clutch for use with a tape winding-up mechanism of a tape recordingand reproducing apparatus. A cylindrical drum is provided on a pulleyfor receiving input force of the clutch and a length of rope is woundaround the drum in frictional torque transmitting sliding engagementtherewith. The rope has opposite ends connected to a disc rigidlysecured to an output shaft of the clutch whereby substantially constanttorque is transmitted from the drum to the disc regardless of variationin coefficient of friction between the driving and driven members.

2 Claims, 10 Drawing Figures P'A'TE'N'TEB SEP 19 I972 sum 1 BF 2 PRIORART VIII INVENTOR ATTORNEY SLIP-CLUTCH BACKGROUND OF THE INVENTION Fieldof the Invention The present invention relates to a slip-clutch used asa frictional torque transmission in a tope take up mechanism of a taperecording and reproducing apparatus and the like.

A conventional frictional torque transmission of this kind employs apair of rotatable member or tape urged against each other by springmeans for the transmission of torque from one of the discs to the other.In general, the coefficient of friction between the frictionally slidingsurfaces of the opposite driving and driven members tends to increasewith the variation in the surface condition due to wear of the surfaces,stain and blot on the surfaces and with the rise of the temperature atthe surfaces. In some remarkable cases, the increase in the frictioncoefficient amounts to two to three times as compared with that innormal or initial operation. The torque transmitted by the conventionalclutch, therefore, varies in proportion to the variation in the frictioncoefficient in prolonged operation of the device. This adversely affectsthe tape winding-up force of the reel supporting and driving wheels sothat, when the friction coefficient is increased, the tape is subjectedto excessive tension with a result that the tape becomes to havepermanent strain and deformation and, in a remarkable case, the tape isbroken. On the other hand, in case where the friction coefficient isdecreased, the tape take-up mechanism becomes inoperative to wind up thetape.

It is, therefore, a principal object of the present invention to providea slip-clutch which is able to provide a stable torque transmissioncharacteristic which is scarecely influenced by the variation in thecoefficient of friction between the frictionally sliding surfaces of theclutch.

The conventional friction clutch has an additional disadvantage that thefrictionally sliding surfaces have therebetween a coefficient offriction which is largely varied with the difference in the direction inwhich the friction members are rotated. This variation gives rise tovarious troubles during practical operation of the clutch for prolongedperiod of time.

Accordingly, it is another object of the present invention to provide abi-directional slip-clutch which can provide a torque-transmissioncharacteristic which is remarkably stable and is hardly varied with thevariation in the friction coefficient between the sliding surfaces dueto the change of the direction of rotation of the friction members.

SUMMARY OF THE INVENTION According to one aspect of the presentinvention, there is provided a slip-clutch including atorque-transmission means comprising a cylindrical body and a length offrictional slider extending around the outer surface of said cylindricalbody in frictional sliding engagement therewith, said slider beingmounted on a support in such a manner that the leading end of saidslider as viewed in the rotation of said cylindrical body in onedirection is connected to said support through a spring means while thetrailing end is directly secured to said support.

According to another aspect of the invention, there is provided abi-directional slip-clutch including a torque-transmission meanscomprising a cylindrical drum member and a length of a rope havingspiral turns extending around said drum in frictional sliding engagementtherewith, spring means for resiliently connecting the opposite freeends of said rope to a support therefor, the leading end of said rope asviewed in the rotation of said drum in one direction causing thecorresponding portion of said spring means to be operative, and stopmeans on said support for being abutted upon by the portion of saidspring means cooperating with the trailing end of said rope as viewed inthe rotation of said drum in the same direction to thereby cause thelast said spring portion to be inoperative, the change-over of thedirection of rotation of said drum serving to automatically render oneof said spring portions operative and render the other spring portioninoperative.

In a preferred embodiment of the present invention, each of thecylindrical body and drum is a part of a pulley which receives the inputforce of the clutch while the support for each of the frictional sliderand the rope is drivingly connected to the output shaft of the clutch.The frictional slider of the clutch according to the first aspect of theinvention may preferably be made of a material having a remarkably smallstiffness and large taff and wear-resistant properties, such as rope offibrous material, thread and belt. The rope of the clutch according tothe second aspect of the present invention may preferably have similarproperties. In addition, the spring means in the clutch according to thesecond aspect of the invention may preferably be a twisted springbecause a spring of this type can have its free ends or arms each ofwhich is positioned substantially in the same radial plane as thecorresponding free end of the rope extending from the spirally woundturns around the cylindrical drum.

The torque-transmission characteristic of the slipclutch according toany of the afore-stated aspects of the invention depends solely upon thecoefficient of friction between the sliding surfaces of the cylindricalbody or drumand the frictional slider or rope and upon the angle overwhich the slider or the rope extends around the outer surface of thecylindrical body or drum. The coefficient of friction and the angle inquestion can easily be determined to be of appropriate values so as toobtain a desired torque-transmission characteristic of the clutch. Thus,the characteristic concerned is made stable and is not influenced withany kind of variation in friction coefficient between the slidingsurfaces of the driving and driven members. In addition, the maximumtorque transmitted by the clutch according to the present invention isdetermined by the resiliency of the spring means used to connect theslider or rope to the support therefor.

The above and other objects and features of the present invention may bemade apparent from the following description of preferred embodiments ofthe invention with reference to the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an axial sectional side view ofconventional slip-clutch mounted in a tape windingup mechanism of a taperecording and reproducing apparatus;

FIG. 2 is a similar sectional view of an embodiment of the slip-clutchaccording to the present invention which is mounted in a similar tapewinding-up mechanism of a tape recording and reproducing apparatus;

FIG. 3 is a cross-section taken along line IlI--III in FIG. 2 andillustrating a cylindrical driving body, a frictionally driven sliderand a support therefor;

FIG. 4 is a view similar to FIG. 3 but illustrates a modification to theclutch shown in FIGS. 2 and 3;

FIG. 5 is an axial sectional side view of another embodiment of theslip-clutch according to the present invention which is mounted in atape winding-up mechanism of a different tape recording and reproducingapparatus;

FIG. 6 is a side view of the clutch of the instant embodiment with apart removed;

FIG. 7 is a cross-section taken along line VII-Vll in FIG. 5 andillustrating the relative position of a cylindrical drum, a rope, aspring, a support for the rope and a pair of stops on the support whenthe latter is rotated in one direction;

FIG. 8 is a view similar to FIG. 7 but illustrates the relative positionof the elements when the support is rotated in the other direction; 1 1

FIG. 9 is a view similar to FIGS. 7 and 8 but illustrates a modificationto the clutch shown in FIGS. 5 to 8; and

FIG. 10 is a graphical representation illustrating the stability of thetorque-transmission characteristic of the clutch of the invention withrespect to the variation in the coefficient of friction between twocooperating friction members of the' clutch and a comparablecharacteristic of a prior art clutch with respect to similar variationin the friction coefficient.

DESCRIPTION OF PRIOR ART Before the embodiments of the present inventionare described, a conventional friction clutch will be described withreference to FIG. I of the drawings. The conventional clutch isillustrated as being mounted in a tape winding-up mechanism of a taperecording and reproducing apparatus having a reel supporting and drivingwheel I mounted on a shaft 2 for free rotation. A tire of rubber 3 issecured to the peripheral surface of the wheel 1. The wheel 1 is sodisposed as to be driven by a wheel or roll 4 which is in frictionalrolling contact with the tire 3. The roll 4 is rigidly mounted on oneend of a shaft 5 which is rotatably supported by a bearing 6 which alsoserves to support a slip-clutch which is described hereafter.

The clutch includes a pulley 7 mounted for free rotation on a hub 10 ofa disc 9 which in turn is rigidly secured to the other end of the shaft5. A disc of felt 8 is disposed between the disc 9 and the pulley 7 andis secured to the disc 9 for rotation therewith. A spring retainer orwasher 11 is mounted for free rotation on the shaft 5 adjacent the endof the bearing 6 remote from the roll 4. A coil spring 12 is mountedaround the shaft 5 and extends between the washer 11 and the pulley 7 sothat the spring 12 resiliently urges the pulley 7 against the felt disc8 with a substantially constant pressure force. The pulley 7 is drivenby means of a belt 13.

The torque transmitted by the clutch described is given by the followingequation:

wherein P is the pressure force of the spring 12, u is the coefficientof friction between the felt disc 8 and the pulley 7, and R is theeffective radius of the frictionally sliding surfaces. The value of thefriction coefficient is varied as the clutch is operated for the reasonsdescribed before. Thus, the torque transmitted is also variedcorrespondingly.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring next to FIGS. 2 to 5 ofthe drawings which illustrate an embodiment of the present invention.The portions similar to those of the conventional device shown in FIG. 1are indicated by similar numerals. The slip-clutch according to theinstant embodiment of the invention includes a pulley 14 having acylindrical outer surface 15. The pulley 14 is mounted for free rotationon a shaft 5 for driving a reel supporting and driving wheel 1 in thesame manner as that in the conventional device. A frictional slider 16is mounted on a support 17 in such a manner that a part of the slider 16extends around a part of the cylindrical outer surface 15 of the pulley14 in frictional sliding engagement with the surface 15 as will be bestseen in FIG. 3. The pulley 14 is rotated in clockwise direction, asindicated by the arrow draw within the circle of the outer surface 15 inFIG. 3. The leading end of the frictional slider 16 as viewed in therotation of the pulley 14 is connected to a spring 20 which in turn issecured to the support 17 as at 21. The trailing end of the slider 16 isdirectly secured to the support 17 as at 19. The support 17 has thereona hub 18 which is rigidly secured to the shaft 5. The frictional slider16 is preferably made of a material having a remarkably small stiffnessand good tensile and wear-resistant properties, such as rope of fibrousmaterial, thread and belt.

With the above arrangement, a part of the torque transmitted from a belt13 to the pulley 14 is transmitted to the support 17 by virtue of thefrictional sliding movement of the outer surface 15 of the pulley 14with respect to the slider 16 so that the support 17 is also rotated inclockwise direction as indicated by another arrow drawn outwardly of thesupport 17 in FIG. 3.

FIG. 4 illustrates a modification to the slip-clutch shown in FIGS. 2and 3. In this modified embodiment of the invention, a frictional slider16 has spiral turns wound around the outer surface 15 of the pulley 14so that the slider extends around the surface 15 over an angle of morethan 360.

Referring to FIGS. 5 to 8 of the drawings, a description will be madewith respect to a second embodiment of the present invention. Theinstant embodiment is directed to a bi-directional slip-clutch which isused as a torque transmission in a tape winding-up mechanism for a taperecording and reproducing apparatus. The tape winding-up mechanismincludes a pair of laterally spaced reel supporting and driving wheels31 and 32 having tires 33 and 34 mounted on the peripheral surfaces ofthe wheels, respectively. A pulley or roll 35 is mounted on one end of ashaft 36 and is positioned to extend between the wheels 31 and 32 Theshaft 36 rotatably extends through a bearing 37 mounted on a support 38which is movably mounted so that the roll 35 can be selectively movedinto frictional rolling contact with one of the tires 33 and 34 of thereel driving wheels 31 and 32 so as to drive the selected wheel for thetake-up of the tape.

The slip-clutch of the instant embodiment of the invention is mounted onthe other end of the shaft 36 and comprises a pulley 39 mounted for freerotation on the shaft 36. The pulley 39 receives the input force of theclutch from a belt 40 which is in driving engagement with the pulley.The latter has a hub or cylindrical drum 41 on the side of the pulley 39remote from the bearing 37.

As will be best seen in FIG. 6, a length of rope 42 is spirally woundaround the drum portion 41 and extends therearound in frictional slidingengagement therewith. The material from which the rope 42 is madeshouldbe determined depending upon the material from which the drum 41is made. The rope 42 is preferably made from a soft fibrous material inthe case where the drum 41 is made from either a plastic material or ametal.

A disc 43 is rigidly connected to a hub 44 which in turn is fixed to theend extremity of the shaft 36 by means of a setscrew 45. On the surfaceof the disc 43 facing the pulley 39, the disc 43 has a pin 47 extendingaxially toward the pulley 39 in spaced relationship to the drum 41. Thepin 47 rotatably receives coiled turns of a spirally twisted spring 46having opposite free ends or arms 48 and 49 each connected to one of theends of the rope 42 extending from the spiral turns thereof, as shown inFIG. 7, so that the twisted spring 46 is rotatably or swingably mountedon the disc 43. The arms 48 and 49 have substantially the same length.Stop pins 52 and 53 are also mounted on the same side of the disc 43 asthe pin 47 and adjacent the end extremities of the spring arms 48 and49, respectively, for the purpose which will become apparent later.

It is desired that the spring employed in the slipclutch according tothe present invention has as smaller spring constant as possible in thata spring having such property exhibits lesser variation in spring forceas caused by the deformation of the spring. A twisted spring issatisfactory to this purpose. The use of a twisted spring in thisinvention provides an additional advantage that the axial spacingbetween the opposite ends or arms of a twisted spring can accommodatethe axial spacing between the ends of the rope spirally wound around thedrum, so that it is possible to simplify the arrangement for holding thespring. In fact, each of the spring arms 48 and 49 (48a and 49a in caseof FIG. 9 embodiment) is positioned to extend substantially in the sameradial plane as the corresponding end of the rope 42.

With the afore-described arrangement, when the pulley 39 is rotated inclockwise direction as shown in FIG. 7, the rope 42 is frictionallydriven by the outer surface of the drum 41 so that the leading end ofthe rope 42 as viewed in the rotation of the drum in this direction ispulled to render the corresponding spring arm 49 operative to serve as aspring while the trailing end of the rope 42 is loosened to allow thecorresponding spring arm 48 to abut against and to be stopped by thestop pin 52. Thus, the spring arm 48 is automatically made inoperativeto serve as a spring. On the other hand, when the pulley 39 is rotatedin counterclockwise direction as shown in FIG. 8, the spring arm 49 isallowed to abut against the stop pin 53 while the other spring arm 48 iscaused to resiliently function.

For any of the directions of rotation, the same magnitude of torque istransmitted by the slip-clutch which employs spring arms 48 and 49 ofthe same length, as shown in FIGS. 7 and 8.

FIG. 9 illustrates a modification to the embodiment shown in FIGS. 5 to8. In this modification, the clutch employs a spring 46a having arms 48aand 490 one (48a) of which is longer than the other (49a). Thedifference in the length of the spring arms causes the clutch totransmit a greater magnitude of torque in one direction of rotation ofthe clutch than in the other direction of rotation thereof.

In the afore-described embodiments of the present invention, the pulleysare disposed on input side of the clutch while the frictional slider andthe rope are on the output side of the clutch. It is, however, to benoted that the same result can be obtained from the reversedrelationship between the cooperating components of each clutch.Moreover, for the purpose of simplification of illustration, the ends ofthe rope 42 are shown as being directly connected to the spring arms 48and 49 (48a and 49a in the case of FIG. 9 embodiment). It is, however,to be understood that additional fittings or joints can of course beutilized to connect the rope ends to the spring arms.

The torque transmitted by the clutch according to the present inventionis mathematically given by the following equations:

F 1 2 (2) wherein e is the base of natural logarithm, u is thecoefficient of friction between the cylindrical outer surface 15 or drum41 and the slider 16 or the rope 42, and 0 is the angle over which theslider 16 or the rope 42 extends around the cylindrical surface 15 orthe drum 41.

1 Thus, F; (3) The equation (3) is substituted for F in equation l Inequation (4), the angle 0, the tension E and the radius R remainconstant throughout the operation of the clutch. It is, therefore,understood that the torque M is determined by the variable representedby which in turn is determined by the variable or the frictioncoefficient u.

FIG. 10 graphically illustrates the relationship between the twovariables. It will be appreciated from FIG. 10 that, when appropriatevalues are selected for the angle 0 and the friction coefficient [1-, atorquetransmission characteristic which is kept stable or substantiallyconstant throughout prolonged operation is obtainable from theslip-clutch of the present invention even if the friction coefficient p.is varied during operation. It will further be understood that theslip-clutch of the invention provides remarkably improved stability intorque-transmission characteristic particularly with respect to theincrease in the friction coefficient. For example, a curve indicated by41rrepresents the torquetransmission characteristic of the clutch of theinvention in the case where the slider 16 or rope 42 is wound around thecylindrical outer surface 15 or drum 41 over an angle of 471-, as in theembodiments shown in Fig. 4 and Figs. 6 to 9. This curve represents avery stable or constant torque-transmission characteristic in the rangerightward of a point P at which friction coefficient p. is equal to 0.3,that is, in the range wherein p. is increased and is more than 0.3. Tothe contrary, a conventional disc type slip-clutch which is designed tohave its coefficient of friction p. on the point P provides atorque-transmission characteristic as represented by a curve A whichextends substantially linearly in proportion to the value of t.

From the foregoing description and illustration, it will be appreciatedthat the present invention provides a slip-clutch whosetorque-transmission characteristic is scarcely influenced by thevariation in the coefficient of friction between two cooperating drivingand driven members but is kept substantially constant and stablethroughout the operation for prolonged period of time.

What is claimed is:

l. A bi-directional slip-clutch including a torquetransmission meanscomprising a cylindrical drum member and a length of a rope havingspiral turns extending around said drum in frictional sliding engagementtherewith, spring means for resiliently connecting the opposite freeends of said rope to a support therefor, the leading end of said rope asviewed in the rotation of said drum in one direction causing thecorresponding portion of said spring means to be operative, and stopmeans on said support for being abutted upon by the portion of saidspring means cooperating with the trailing end of said rope as viewed inthe rotation of said drum in the same direction to thereby cause thelast said spring portion to be inoperative, the

change-over of the direction of rotation of said drum serving toautomatically render one of said spring portions operative and renderthe other spring portion inoperative.

2. A bi-directional slip-clutch as defined in claim 1, wherein saidspring means comprise a twisted spring number having spirally twistedturns operatively connected to said support and opposite free endsextending from said turns for being connected with the opposite ends ofsaid rope, respectively, each of said spring ends being positionedsubstantially in the same plane as the corresponding end of said rope.

1. A bi-directional slip-clutch including a torque-transmission meanscomprising a cylindrical drum member and a length of a rope havingspiral turns extending around said drum in frictional sliding engagementtherewith, spring means for resiliently connecting the opposite freeends of said rope to a support therefor, the leading end of said rope asviewed in the rotation of said drum in one direction causing thecorresponding portion of said spring means to be operative, and stopmeans on said support for being abutted upon by the portion of saidspring means cooperating with the trailing end of said rope as viewed inthe rotation of said drum in the same direction to thereby cause thelast said spring portion to be inoperative, the change-over of thedirection of rotation of said drum serving to automatically render oneof said spring portions operative and render the other spring portioninoperative.
 2. A bi-directional slip-clutch as defined in claim 1,wherein said spring means comprise a twisted spring number havingspirally twisted turns operatively connected to said support andopposite free ends extending from said turns for being connected withthe opposite ends of said rope, respectively, each of said spring endsbeing positioned substantially in the same plane as the corresPondingend of said rope.